1. Field of the Invention
The present invention relates to a driver circuit for driving scan lines or signal lines in a display device.
2. Description of the Related Art
Plane display devices, typified by liquid crystal display devices, feature thinness, light weight, and low power consumption, and accordingly are in use for displays of various types of electric appliances. Out of the plane display devices, active-matrix liquid crystal display devices with a transistor arranged in each pixel have been increasingly in use for note personal computers and portable information terminal devices. Recently, a technique has been established, which forms polysilicon thin film transistors (p-Si TFTs) with high electron mobility by means of a process to be performed at a temperature relatively lower than that which is applied in order to form amorphous silicon thin film transistors, which have been in use for conventional liquid crystal display devices. This establishment has made it possible to fabricate transistors in a smaller size, which are in use for liquid crystal display devices. This has made it possible to integrally form a pixel part and driver circuits on a transparent glass substrate through a single manufacturing process: the pixel part is configured by arranging a transistor at an intersection between each of a plurality of scan lines and its corresponding one of a plurality of signal lines, and the driver circuits respectively drive a group of scan lines and a group of signal lines.
In addition, as disclosed in Japanese Patent Laid-open No. 2003-344873, development has been in progress for a bootstrap circuit for the purpose of setting electric potential for output signals from a driver circuit at a sufficient level.
An electric potential difference between the high-level voltage and the low-level voltage of output signals from a driver circuit is used in order for the output signals from the driver circuit to control the writing of video signals into each pixel. For this reason, from the viewpoint of enabling the writing to be stable, it is desirable that the electric potential difference be as large as possible. However, a larger electric potential difference between the high-level voltage and the low-level voltage means a higher voltage stress being on the transistors. This is likely to reduce reliability in operation of each of the transistors that constitute the driver circuits. Furthermore, the larger electric potential difference leads driving the driver circuits at a higher voltage. This brings about a problem of requiring larger power consumption.